1. Field of the Invention
The present invention relates to a transportation system and to a method for backing up the operational state of a transportation system.
2. Background of the Invention
In transportation systems, such as an elevator system, usually battery backup is used in order to enable selected system functions to be maintained even during a power failure. If an elevator car is carrying passengers at the onset of a power failure, battery backup can be used to maintain a communication connection from the elevator car to a maintenance center; similarly, power can be supplied from the battery for illumination of the elevator car. For such purposes, the battery is generally fitted in conjunction with the elevator car, e.g. on the top of the elevator car.
One of the problems with battery backup is unreliability of batteries. Batteries deteriorate in a short time, and the number of charge/discharge cycles they can tolerate is quite limited. Moreover, e.g. ambient temperature has an effect on the service life of batteries and also restricts their service conditions.
In many types of electronic applications, there has in recent years emerged the use of so-called supercapacitors, which are also called ultracapacitors or double-layer capacitors. There are different types of supercapacitors, depending on the principle and material of manufacture, but a feature characteristic of all these is a high energy storing capacity. As compared to conventional capacitors, the square area of the charge surfaces of supercapacitors has often been increased by using active carbon or some other solution increasing the square area. Supercapacitors usually have an energy storing capacity several tens or even hundreds of times higher as compared to conventional capacitors.
Publication JP 9322430 proposes an arrangement that uses a battery with a supercapacitor fitted in parallel with it in order to reduce the number of battery charge/discharge cycles so as to increase the service life of the battery.
Publication JP 7271681 proposes a solution where power is supplied to a semiconductor memory device from a battery or alternatively from a supercapacitor.